1. Field of the Invention
This invention relates to the field of corrosion inhibition. More particularly, the invention relates to the inhibition of corrosion of metals commonly used in the fuel distribution and handling systems for internal combustion engines, especially where the fuel is alcohol and the engine is used to power motor vehicles.
Alcohols have, in the past, been used as extenders and replacements for petroleum fuels in internal combustion engines. Thus, "gasohol" fuel is becoming increasing familar as an engine fuel in the United States. If oil supplies become less available in future years, it is anticipated that alcohols may gradually replace petroleum fuels in internal combustion engines. In Brazil, for example, ethanol is widely used as fuel for internal combustion engines. In the United States, both methanol and ethanol have been considered for supplementation or replacement of petroleum fuels.
The use of alcohols, such as ethanol, as a replacement fuel for petroleum in internal combustion engines presents corrosion problems not heretofore encountered in petroleum fueled internal combustion engines. Thus, alcohol fuels present corrosion problems throughout their storage and distribution systems. The corrosion problem, for example with ethanol, is mainly due to the presence of a small amount, i.e., 3 to 9%, of water in the alcohol which is not removed during normal distillation processes. Although it is possible to remove this residual amount of water by a final distillation step, the cost is inordinately high. Accordingly, some processors do not normally remove the last amounts of water in the alcohol and the presence of such water enhances corrosion of metals with which the alcohol comes in contact. Further, impurities in the alcohol, such as chloride ions and acetic acid, also contribute to the corrosive effects of alcohol on metals it contacts during its transportation in the field and its use in the fuel systems of internal combustion engines.
Since alcohols come into contact with a variety of metals during their preparation, storage, distribution and transportation and within the fuel system of an internal combustion engine, corrosion scientists are faced with complex problems in the effort to inhibit corrosion in a system composed of various metals.
2. Prior Art
The most common metals encountered in the fuel systems of vehicles powered by internal combustion engines are alloys of zinc, copper, iron, tin, steel and aluminum. Most commonly, alloys such as ternplate, brass, steel and Zamak (an alloy of zinc, copper and aluminum) are encountered.
A variety of chemical corrosion inhibitors have been used to inhibit corrosion in metals such as zinc, steel, copper, etc. Such inhibitors include aliphatic and aromatic amines, amine salts of acids such as benzoic acid, hetercyclic amines such as pyridines, alkenyl succinic acids, triazoles such as benzotriazole and the like. Such inhibitors have been used in such media as salt water, acids and alkali. Other inhibitors which have been used include hydrogen sulfide, metal salts such as sodium chromate, sodium silicate, ferrous nitrate, ammonium phosphate, potassium dichromate, sodium borate, sodium phosphate, sodium nitrate, and sodium chlorate, glucose, borax, formamide, rosin amine, propargyl ether, propionic acid, valeric acid, quaternary amine salts, alkanolamines, aminophenols, alkyl and aryl mercaptans and the like. A comprehensive summary of corrosion inhibitors is set forth by M. Brooke, "Chemical Engineering", Feb. 5, 1982, pages 134 through 140 and by C. C. Nathan, Corrosion Inhibitors, (NACE), 1973.